QUANTITATIVE SURVEY OF THE 

 BENTHOS OF SAN PEDRO BASIN, 

 SOUTHERN CALIFORNIA 



Part I. Preliminary Results 



INTRODUCTION 



This report outlines the preliminary results of a quantitative study 

 of the marine animal populations in a limited area of southern California. 

 The purpose of the project has been to conduct an intensive survey of the 

 benthic invertebrate metazoan animals of San Pedro Basin, and to at- 

 tempt a reconstruction of the natural animal associations. Many of the 

 physical features, including temperature and salinity of the Basin, are 

 known or are being investigated by the geologists and oceanographers 

 of southern California. In time, therefore, the biological and physical 

 data may be correlated and many features of distribution and abundance 

 explained. 



Throughout the San Pedro Basin, measured samples have been taken 

 at chosen intervals for more than two years (1952 to 1954), using a 

 bottom sampling device that grabs a sizeable part of the sea bottom 

 from any depth. The device is dropped as a plummet, presumably without 

 obliquity; its measured descent is used to indicate depth to the bottom. 

 The sample is hauled up and immediately deposited in a large tub that 

 completely accommodates the contents of the grab, in as undisturbed a 

 condition as possible. Two half-pint samples are removed and set aside 

 for future physical studies. From the tub the material is transferred to 

 a set of screens of selected sizes. Care is taken that the innumerable soft- 

 bodied animals remain as intact as possible. The screens, with mesh from 

 coarse to fine, measuring to 24 meshes to the inch, sort out the animals 

 and other particles; they are washed with seawater and preserved with 

 a reagent (formalized seawater) to harden protoplasmic tissue. Finally 

 the labeled samples are taken to the laboratory, where all subsequent 

 work is done. Tyler Standard screens, with meshes to a fine of Z2 to the 

 inch, are used for further washing of the samples. They are sorted and 

 analyzed, then transferred to 70% alcohol. 



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